Most people are familiar with the concepts of the Yummy Mummy – the gym-toned career woman with child who manages to stay fanciable – and the Glamorous Grandmother, a vast cross-section of mature lipsticked women whose most prominent member is Lady Sonia McMahon, wife of former prime minister Billy, photoshoped to within an inch of her adolescence during last year’s ad campaign for fashion label Charlie Brown. How, though, do you categorise Mary Shackman? A white-haired textile designer, painter, mother and grandmother, Shackman posed for the cover of Sunday Life magazine last year clad in nothing but an eiderdown. She looked marvellous – kooky, but marvellous.

“I always like a challenge,” says Shackman, an unwitting pin-up for the 60-plus set. At the time of her debut with doona Roger Michell’s provocative film The Mother was screening in cinemas, causing a furore with its frank depiction of a mature woman bedding a much younger man. “It was quite good,” says Shackman. “I’d seen it.” So when she was asked to do some modelling for a story on mature women and sexuality, she said yes. “Then they decided to interview me, sounding like a great champion for older women having sex. I didn’t mind. Am I brave? Well, I’m game.”

The fashion world favours youth and a certain kind of Stay-Press beauty. Eccentric dowager types such as Italian Vogue’s venerable fashion editor Anna Piaggi – who looks like a cross between the poet Edith Sitwell and a kabuki player – are embraced. Less theatrically styled older women are shunted aside in favour of leggy Latvian models barely out of nappies. In this context, Shackman is an extraordinary exception. She is content not only to live in her own Botox-free skin but to have it photographed in the looks of the new season. For her latest trick, she modelled an outfit by Akira Isogawa in Shop Til You Drop magazine’s September issue.

Today she is working on canvases for her upcoming exhibition, inspired by the pixelated faces of crime victims on the news. She looks studiedly casual in skinny denim jeans, Converse sneakers and a doodle-covered T-shirt by Wild & Lethal Trash, a Belgian streetwear label. Her long hair is swept up in a girlish ponytail, revealing dangly earrings and cheekbones worthy of 1960s model Veruschka. “I remember someone at a party once talking about America, saying they’d keep seeing these women with gorgeous long hair, good figures and all that from the back, then the woman turns round and … ahhhh my God – they’re so old! So I tried short hair but I loathed it. Then I thought bugger it. It’s so boring.”

Shackman was born in San Francisco, where her American airman father was based. Alexander Shackman fell for Mary’s mother, also Mary, while on leave in Brisbane, and for the first eight years of their marriage they travelled back and forth between Sydney and the US. It sounds suitably bohemian, except that Mr and Mrs Shackman were “terribly normal. Dad was an engineer and I had quite a regular upbringing, apart from the fact that I moved schools a lot. When we finally settled down in Double Bay I could barely read and write – but I knew all about eating in restaurants.”

Last month Shackman – in a hand-painted, multicoloured dress and a lot of zany, architectural jewellery – threw a birthday party in her stately Paddington house. It was attended by her 30-year-old son Josh and a throng of Sydney art-world players, plus some much younger fashion people. “I think the young designers are so interesting,” she says. “Anyway, everyone my age is probably retiring.” Adorning the invitation was a picture of Shackman in the 1970s, sporting a giant fur coat, micro mini and sunglasses worthy of Elton John.

Back then, she designed textiles to make a buck. She had landed at the National Art School in Darlinghurst in 1960 after a stint at Miss Hale’s secretarial school failed to light her fire. She’d spent her teens at a private boarding establishment in Bowral and was “useless at everything” except painting. “Then I got to college and embraced this new crowd. I remember the art teacher telling us: ‘Don’t worry if you see girls in plastic raincoats with nothing underneath.’ He meant the life-drawing models, of course, but at the time it seemed very exciting and adventurous.”

In 1967 Shackman and another student started making fabrics and selling them. She claims they were hopeless amateurs: “Having only printed one-offs for art projects, we didn’t have a clue about how to set out a formal print for fabric. We just painted on the screen with a lacquer as though it was nail polish.” Soon they were stocking the fabric departments of all the big stores. They supplied Carla Zampatti and Melbourne’s The House of Merivale and Mr John boutiques – once the place for office girls to pick up bell-bottoms. For Jenny Kee, she of the kitsch Australiana prints, Shackman re-interpreted Aboriginal crocodile paintings in bright colours “until everybody realised it was politically incorrect”. By the mid-’70s she was “up to my ears in fabric”, painting T-shirts for Sportsgirl and flogging the extras off at Paddington Markets. Australian Vogue’s Nancy Pilcher was a customer and gladly spruiked Shackman’s wares overseas. By now she was entrenched in the rag trade. Secretly, though, she hankered after a gallery presence.

One day she painted a bunch of old chairs that were collecting dust in her studio, then some screens and tables. Once she’d painted all her furniture with her now signature candy-coloured grids – think Bridget Riley, but looser-limbed after a slew of martinis – she finally went back to canvas. And these days she rarely paints a bolt of cloth.

The fashion world, however, refuses to retreat. “I still love fashion people.” She points to a small pink and apple-green painting on her kitchen wall. “That was inspired by Michelle Jank’s hair,” she explains, referring to the 28-year-old Australian designer who until recently sported a pastel pink mop. Last year Shackman painted silk for a line of handbags by London accessories designer Anya Hindmarch. She painted a frock that Delta Goodrem wore on her last tour. “It looked fantastic,” she says. “You have to keep yourself busy doing different things. I couldn’t bear to retire; I’d be terribly bored. And boredom isn’t really me, is it?”

Most people are familiar with the concepts of the Yummy Mummy – the gym-toned career woman with child who manages to stay fanciable – and the Glamorous Grandmother, a vast cross-section of mature lipsticked women whose most prominent member is Lady Sonia McMahon, wife of former prime minister Billy, photoshoped to within an inch of her adolescence during last year’s ad campaign for fashion label Charlie Brown. How, though, do you categorise Mary Shackman? A white-haired textile designer, painter, mother and grandmother, Shackman posed for the cover of Sunday Life magazine last year clad in nothing but an eiderdown. She looked marvellous – kooky, but marvellous.

“I always like a challenge,” says Shackman, an unwitting pin-up for the 60-plus set. At the time of her debut with doona Roger Michell’s provocative film The Mother...